Exam MCCQE Topic 1 Question 96 Discussion

Actual exam question for Medical Council of Canada's MCCQE exam
Question #: 96
Topic #: 1
A 32-year-old primigravid woman is receiving magnesium sulfate for tocolysis. Her pregnancy is at 26 weeks' gestation. You suspect magnesium sulfate toxicity. Which one of the following is the first sign of magnesium sulfate toxicity?

Suggested Answer: A Vote an answer

Magnesium sulfate toxicity is dose-dependent. The earliest and most sensitive clinical sign is theloss of deep tendon reflexes (especially patellar), which occurs before respiratory depression or cardiac changes.
Toronto Notes 2023 - Obstetrics Chapter:
"Toxicity from magnesium sulfate is progressive and typically presents first with loss of deep tendon reflexes.
Respiratory depression and cardiac arrest occur at higher serum levels. Regular monitoring of reflexes, respiratory rate, and urine output is essential." MCCQE1 Objectives (Obstetrics > 83-3: Preterm Labour and Tocolysis):
"The candidate must recognize early signs of magnesium sulfate toxicity including areflexia and respiratory depression." Tachycardia (B), hypotension (C), and tachypnea (D) are not typical early signs. Oliguria (E) may be a risk factor for accumulation but is not the first sign of toxicity.

by Isidore at Aug 14, 2026, 04:36 AM

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